Abstract

The 1999 November 12 Duzce earthquake (M (w) = 7.1) was apparently the eastward extension of the August 17, Izmit earthquake (M (w) = 7.4). The Duzce event caused heavy damage and fatalities in the cities of Duzce and Bolu. Here a finite-fault inversion method with five discrete time windows is applied to derive the co-seismic slip distribution of the Duzce earthquake. The fault plane is best modelled as a 40 x 20 km(2) plane, with a strike of 262degrees and a dip of 65degrees to the north, and that the majority of slip occurred in two distinct patches on either side of the hypocentre, implying bilateral rupture. The possible triggering of this event by the Izmit earthquake is investigated using Coulomb stress modelling of all large events since 1943 with the inclusion of secular loading. The results show that although the Duzce rupture plane was in a stress shadow prior to the Izmit earthquake, that event caused a significant Coulomb stress load, taking the Duzce fault out of the stress shadow, which probably precipitated failure. A comparison of the mapped Coulomb stress change with the inferred slip shows no correlation between the two. Finally, the stress modelling indicates that the northern branch of the North Anatolian fault zone, beneath the Sea of Marmara towards the city of Istanbul, is presently the most highly loaded segment of the North Anatolian Fault Zone.